Memory integrity is a critical factor for a wide variety of integrated circuits. Memory errors, which affect memory integrity, are a significant concern in system applications because they may affect a process operation. For example, control or operating programs and input/output (I/O) decisions are typically stored in RAM and precisely direct physical operations of the system. If an input bit were to suddenly change due to a memory error, the control program may react to the changed input by erroneously turning on or off a key output. Depending on the nature of the output change, undesirable consequences may occur. Likewise, if a control program bit were to change unpredictably, the device may execute a random and/or unpredictable sequence—this again may lead to undesirable results. In devices such as programmable logic devices (PLDs), corruption of a bit in the memory that configures the configurable logic resources is also a critical concern. Thus, for robust systems design, memory error detecting systems are generally necessary to ensure memory integrity.
The classical approach to detection and correction of errors is by use of an error correction code (ECC). An error correction code associated with a slice of data is stored. If an error is detected when memory is read, correction algorithms may be applied to the faulty data in conjunction with stored ECC codes, and in some cases, data may be restored. One such class of ECC correcting algorithms include utilization of “Hamming Codes” which are employed to detect and correct errors that may have occurred.
The application of error detection and correction schemes present cost challenges to systems designers as conventional ECC memory subsystems require additional memory devices, which increase component costs and board area. An additional drawback to conventional schemes is the inefficiency of byte write operations. This is due to the need to read all data supported by the encoding, updating this structure with the modified byte, updating the ECC code, and then writing this entire structure back to memory (i.e. Read/Modify/Write).
It can be seen then that there is a need for a method, apparatus and program storage technique that provides an error correction code memory system with a small footprint and efficient byte write operations.